The objective of the project is to study the effects of intermittent retractive and protractive heavy ("orthopedic") forces on the maxilla in the growing Saimiri sciureus. Special emphasis will be placed on the long-term effects after discontinuation of force application. The longitudinal influence of force application on the craniofacial morphology will be examined with roentgenographic cephalometry, using metallic implants and in vivo bone markers. The sample consists of twelve growing male squirrel monkeys of known chronological age. The monkeys are divided into three groups, two experimental, and one control; with four monkeys in each group. The monkeys in one experimental group are subjected to a retractive force, and the monkeys in the other experimental group are subjected to a protractive force. Starting when the animals were approximately 12 months of age, the traction will be applied for a period of 6 months (treatment period). Using cemented gold splints on the maxillary teeth and restraining collars for force attachments, a force of approximately 75 grams is being applied intermittently for about 14 hours/24-hour period. The control monkeys have gold splints and restraining collars but no traction. Tantalum implants, oxytetracycline and Procion dyes are used as identification markers in all animals. Lateral cephalometric radiograms will be taken during force application and a 12-month posttreatment observation period. At the end of the observation period, all animals will be sacrificed. The results will be based on histological examination, serial superimposition of cephalometric tracings and cephalometric linear and angular measurements, and dry skull morphology. This research is currently in progress. The application is submitted in order to solicit financial support for the time period involving the last part of the posttreatment observation period and a subsequent period for preparation, analysis and interpretation of data.